A Cone rating means that you can fire that clay using a kiln at any temperature UP TO that cone. The closer you get to the maximum rated cone, the stronger and denser your clay will be. You cannot fire a clay HIGHER than its maximum rated Cone, or it will melt.
For example: Cone 10 clay can be used at low fire (Cone 04-06 or at Cone 6). But to reach its maximum strength the clay should be fired to Cone 10. That will cause the clay to shrink and become dense, and that is ideal, especially for dinnerware projects. (You can see the low absorption numbers below on the porcelain and stoneware clay; for dinnerware you want less than 3%.) For sculpture you often want LESS shrinkage, and absorption doesn't matter. So then firing Cone 10 clay at a lower temperature is ideal. Sculpting clay is designed to have more "open" bodies so they don't get as dense as other clays. An advantage of using Cone 10 clay is that you don't have to worry about over firing your clay if you forget what Cone it is. For this reason, many studios and schools only allow Cone 10 clay to be used for ceramic projects. Cone 10 clay is also typically used for Raku, even though Raku is a low temp process. Clays such as WSO have good temperature shock absorption which is needed for Raku.
Mid-fire stoneware and porcelain, which are the Cone 5-6 clays listed here, can also be used at low fire or up to Cone 6. (Just not above Cone 6.) Everything mentioned about absorption above applies here too. For dinnerware it is best to use a Cone 5-6 clay if you fire to Cone 5-6.
Low-fire clay can only be fired up to Cone 04, or sometimes a little higher. Unlike mid and high fire, it never shrinks much or gets really strong and dense even when fired to its maximum temperature. The main advantage to using a low-fire clay when low firing is that your glazes may craze less than if you used a Cone 6 or Cone 10 clay.
Remember, you have to fire your glaze to the Cone that is specified for that glaze, regardless what clay you use. Just make sure you use a clay rated at least as high as the glaze.
Once you choose a particular cone of clay to use, you have decide on the specific clay body. We list what application each clay body is best for. Usually you use smooth clay when throwing on the wheel, particularly for smaller projects like dinnerware. But for handbuilding, sculpting, and other larger projects, you use clay with more grit (grog or sand.)